Blends of polyphenylene ether resins and styrene-tert-butylstryene copolymers

ABSTRACT

Homogeneous blends of polyphenylene ether resin and copolymers of styrene and 4-tert-butylstyrene are described. Rubber modifiers can be included in the copolymer or the blend. The blends are moldable into highly ductile articles having higher heat distortion temperature.

CROSS-REFERENCE TO RELATED APPLICATION

This is a division of application Ser. No. 327,440 filed Dec. 4, 1981,now U.S. Pat. No. 4,389,511.

BACKGROUND OF THE INVENTION

The polyphenylene ether (also known as polyphenylene oxide) resins are awell known family of engineering plastics capable of being extruded,molded or otherwise shaped into articles of various shapes and sizes. Anumber of these resins and methods for their perparation are disclosedby Allan Hay in U.S. Pat. Nos. 3,306,874 and 3,306,875, and by GeluStamatoff in U.S. Pat. Nos. 3,257,357 and 3,257,358.

It is known from Cizek, U.S. Pat. No. 3,838,435, and elsewhere, thatpolyphenylene ethers and admixable with polystyrene to form blendshaving good properties.

Blends of polyphenylene ether and poly(4-tert-butylstyrene) inparticular, after molding, have been found to be too brittle, with lowtensile strength.

INTRODUCTION TO THE INVENTION

The discovery has now been made that certain copolymers of4-tert-butylstryene and styrene, unmodified or modified with rubber, canbe blended with polyphenylene ether resin to produce a homogeneous(single phase) thermoplastic composition which can be molded into aductile material having good tensile strength and good impact strength.Moreover, the composition has a higher heat distortion temperature (HDT)than the corresponding composite made with polyphenylene ether andpolystyrene.

The copolymers useful in the present kinds of compositions are those inwhich the tert-butylstyrene content is in the range between 5% and 65%by weight, based on the total weight of the copolymer without the rubbermodifier. Copolymers containing less than 5% of tert-butylstyrene do notsignificantly improve the heat distortion temperature of the blend,while copolymers having greater than 65% of tert-butylstyrene result inblends which after molding are brittle, with very low impact strength.The sharp drop in properties which occurs with use of atert-butylstyrene content of greater than 65% is believed due to theincompatibility of such copolymers with polyphenylene ether resin; theblends are not homogeneous, but rather comprise two distinct phases. Thestyrene-t-butylstyrene copolymers can be modified with rubber to improvethe ductility and impact strength of the composition.

The specified styrene-tert-butylstyrene copolymers are not compatiblewith polystyrene alone, and blends of these copolymers with conventionalrubber modified high impact polystyrene (hereinafter also "HIPS") havelower impact strength in the moldings than blends of the same HIPS withpolystyrene homopolymer. However, the further discovery has been madethat addition of polyphenylene ether resin produces a homogeneousmatrix, i.e., a single phase, and properties of the resultant blend ofpolyphenylene ether resin, styrene-tert-butylstyrene copolymer and HIPSare equal to those of blends with the same rubber and polyphenyleneether concentration made with polystyrene homopolymer in place of thestyrene-t-butylstyrene copolymer.

DESCRIPTION OF THE INVENTION

The polyphenylene ether resins useful in accordance with the presentcompositions are well known and readily available.

The preferred polyphenylene ethers are homo- and copolymers of theformula: ##STR1## wherein Q, Q', Q" and Q"', are independently selectedfrom the group consisting of hydrogen, hydrocarbon radicals,halohydrocarbon radicals having at least two carbon atoms between thehalogen atom and the phenol nucleus, hydrocarbonoxy radicals andhalohydrocarbonoxy radicals having at least two carbon atoms between thehalogen atoms and the phenol nucleus, and Q', Q" and Q"' in addition maybe halogen with the proviso that Q and Q' are preferably free of atertiary carbon atom; and n represents the total number of monomerresidues and is an integer of at least 50.

Especially preferred is poly(2,6-dimethyl-1,4-phenylene) ether.

The compositions can also contain, as an optional ingredient, a rubbermodified high impact polystyrene. The terminology "rubber modified highimpact polystyrene" is used in this disclosure in its conventional senseto refer to a well known class of materials, methods for the preparationof which are known. Examples are Foster Grant's FG 834 HIPS and Amoco's6H6 grade of HIPS.

This invention thus provides thermoplastic compositions suitable formolding which comprise polyphenylene ether resin with or without rubbermodified high impact polystyrene, and a rubber modified copolymer ofstyrene and tert-butylstyrene; or composition which comprisespolyphenylene ether resin and styrene-t-butylstyrene copolymer, with orwithout rubber modified high impact polystyrene.

The rubber modified styrene-tert-butylstyrene copolymers which areuseful in the present kinds of compositions can be made by theprocedures known for preparing conventional rubber modified high impactpolystyrene (HIPS).

By way of illustration, in one procedure styrene and tert-butylstyrenein the relative amounts desired for the finished copolymer areco-polymerized by heating in the presence of a radical forming catalyst,e.g., a peroxide, and a rubber, to form a pre-polymer. Polymerization isthen continued in suspension in water. The resultant polymer willcomprise a copolymer of styrene and tert-butylstyrene in approximatelythe original relative proportions and an amount of the rubber.

The resinous ingredients are combinable in virtually all proportions inthe compositions. In the preferred forms, however, the weight percent ofpolyphenylene ether resin to total resin weight varies from 10 to 90percent.

The compositions can optionally also include additional resins tofurther modify physical and chemical properties. Such modifying resinsas are described in Cizek, above, are useful, including linear, block orrandom copolymers of styrene an elastomeric materials, e.g., isoprene orbutadiene. The additional resins include, by way of illustration,styrene containing copolymers such as styrene-acrylonitrile copolymers(SAN), styrene-butadiene copolymers, styrene-maleic anhydridecopolymers, styrene-acrylonitrile-butadiene terpolymers (ABS), blockcopolymers of the A-B-A and A-B type where A is, for instance,polystyrene and B is, for instance, polybutadiene or polyisoprene,radial teleblock copolymers of these two materials, as well ashydrogenated forms of the block or radial teleblock copolymers in whichthe aliphatic unsaturation has been reduced, and acrylic resin modifiedstyrene-butadiene copolymers.

The molding compositions of the invention can and advantageously docontain one or more of the supplementary non-resinous agents which haveheretofore been customarily present in polyphenylene ether resin moldingcompositions to improve certain other physical and chemical propertiesof the moldings. The agents include flame retardants, plasticizers,anti-oxidants, strengthening fibers (for example, glass fibers andgraphite whiskers), mineral fillers/reinforcements, abrasion resistantcomponents, dyes, and pigments. Many of such agents are disclosed inU.S. Pat. No. 4,172,929 to Cooper, et al.

The supplementary non-resinous agents are present in total amount ofbetween about 1% and 50%, on a weight basis, so as to provide thebenefits which these materials have conferred in the past on shapedmolded articles made from thermoplastic resins.

For applications where flammability is important, the optimum copolymercomposition is from 5 to about 40% by weight of tert-butylstyrene.Copolymers containing 25% of tert-butylstyrene yield blends withpolyphenylene ether resin which have a flammability equal to or slightlybetter than blends of the polyphenylene ether with polystyrene, but at50% or more of tert-butylstyrene the blends have poorer flammabilitythan blends with polystyrene. Blends of polyphenylene ether andcopolymer of 25% tert-butylstyrene and 75% styrene, for instance, havegood flammability and physical properties and increase the heatdistortion temperature by about 20° F.

The compositions can be prepared by any of a number of procedures. Inone such procedure the components are dry blended, fed through a singlescrew Brabender or twin screw Werner-Pfleiderer extruder, cut or groundinto particles and fed to an injection molding device.

The invention is further illustrated in the examples which follow. Theseexamples are not to be construed as limiting the invention to theparticular forms shown there, but rather are intended as preferred orbest embodiments. Parts are by weight unless stated otherwise.

EXAMPLE 1

Preparation of a Rubber-Modified Copolymer of Styrene andtert-Butylstyrene

A solution of 90 g of Taktene 1202 poly(butadiene) rubber in 455 g ofstyrene and 455 g of tert-butylstyrene (Dow Chemical Company Monomer No.CX2290; 95% para, 5% meta) was transferred to a one-gallon stainlesssteel reactor along with 0.6 g of benzoyl peroxide and 0.6 g of dicumylperoxide. The reactor was purged with nitrogen and the contents wereheated, while being stirred at 700 rpm by a turbine blade agitator, for41/2 hours at 90° C. (styrene conversion 28%). The prepolymer wastransferred by a gear pump to a second reactor and suspended in 2000 mlof water containing 4.8 g of poly(vinyl alcohol) and 3.6 of gelatin.Polymerization was completed by heating the suspension for 5 hours at100°, 5 hours at 120°, and 6 hours at 140° C. The mixture was cooled andthe product, beads of a 50:50 copolymer of styrene and tert-butylstyrenecontaining 9 % rubber, was filtered off, washed with water and dried.

This procedure was repeated with proportions of styrene andtert-butylstyrene varied to obtain a 25:75 copolymer and a 75:25copolymer.

EXAMPLE 2

A mixture of 55 parts of poly(2,6-dimethyl-1,4-phenylene ether) resin(General Electric's PPO), 45 parts of tert-butylstyrene copolymerprepared as described in Example 1, 1.5 parts of polyethylene, 3.5 partsof triphenyl phosphate, 1 part of diphenyl decyl phosphite, 0.15 part ofzinc sulfide and 0.15 part of zinc oxide was extruded in a 28 mmtwin-screw extruder and the extruded pellets were molded into standardtest pieces by means of a screw injection molding machine. Propertiesare listed in Table 1.

                  TABLE 1                                                         ______________________________________                                        % Tert-                                                                       Butyl-                                                                        styrene                                    Ave.                               in Co- Elong.  Izod (ft.                                                                              Gardner                                                                              HDT         Burn                               polymer                                                                              %       lbs./in.)                                                                              (in. lbs.)                                                                           (°F.)                                                                        UL-94 (sec.)                             ______________________________________                                         0*    50      3.6      110    250   V-1   16.0                               25     60      3.1      100    270   V-1   13.4                               50     32      2.9      125    283   drip  37                                 75     7       0.6      <5     279   drip  80                                 ______________________________________                                         *Amoco 6H6 HIPS; control experiment                                      

The blends have good tensile strength, impact strength and ductility upto a copolymer composition of 50% tert-butylstyrene, with heatdistortion temperatures substantially higher than that of a blendcontaining ordinary rubber-modified polystyrene. Physical propertiesdropped sharply when the tert-butylstyrene content of the copolymer wasincreased to 75%. Flammability of the blend made with the copolymercontaining 25% tert-butylstyrene was as good as that of the controlblend, but flammability was substantially worse than the control forblends made with copolymer containing 50% or more of tert-butylstyrene.

EXAMPLE 3

A mixture of 40 parts poly(2,6-dimethyl-1,4-phenylene ether), PPO, 60parts of rubber-modified copolymer prepared as described in Example 1,1.5 parts of polyethylene, 8 parts of triphenyl phosphate, 1 part ofdiphenyl decyl phosphite, 0.15 part of zinc sulfide and 0.15 part ofzinc oxide was extruded and molded as described in Example 2. Propertiesare listed in Table 2.

                  TABLE 2                                                         ______________________________________                                        % Tert-                                                                       Butyl-                                                                        styrene                                    Ave.                               in Co- Elong.  Izod (ft.                                                                              Gardner                                                                              HDT         Burn                               polymer                                                                              %       lbs./in.)                                                                              (in. lbs.)                                                                           (°F.)                                                                        UL-94 (sec.)                             ______________________________________                                        0      41      4.2      110    211   drip  24                                 25     31      3.5      100    228   drip  17                                 50     24      2.9       75    239   drip  72                                 75     7       0.6      <5     241   drip  90                                 ______________________________________                                    

EXAMPLE 4

Copolymers of styrene and 4-tert-butylstyrene were prepared by theprocedure described in Example 1, but with no rubber present. Equalweights of poly(2,6-dimethyl-1,4-phenylene ether) (PPO) and thetert-butylstyrene copolymer were dissolved in toluene, and the polymerswere co-precipitated by adding the toluene solution rapidly to a largevolume of rapidly stirred methanol. The co-precipitated polymer wasfiltered off, dried in vacuum, and compression molded into film at <500°F. A film was also prepared from a co-precipitated 1:1 mixture ofordinary polystyrene with a 50:50 copolymer of styrene andtert-butylstyrene. The films were tested in a Perkin Elmer DSC-IIdifferential scanning calorimeter, at a heating rate of 40° C./minute,with the results listed in Table 3 below; a single transition indicatesa homogeneous blend, while two transitions show the presence of twodistinct phases.

                  TABLE 3                                                         ______________________________________                                        Glass Transition Temperatures of 50:50 Blends of Tert-                        Butylstyrene with other Polymers                                              Copolymer Composition                                                         (% Tert-Butylstyrene)                                                                         Second Polymer                                                                             Tg (°C.)                                  ______________________________________                                        0               PPO          141                                              25              PPO          158                                              50              PPO          169                                              75              PPO          173 & 194                                        100             PPO          160 & 210                                        50              Polystyrene   98 & 121                                        ______________________________________                                    

EXAMPLE 5

A mixture of 40 parts of a conventional high impact polystyrenecontaining 19.7% of rubber, 60 parts of styrene-4-tert-butylstyrenecopolymer and 0.2 part of Irganox 1076 hindered phenolic antioxidant wasblended in a twin-screw extruder. Blends were prepared from copolymerscontaining 25%, 50% and 75% tert-butylstyrene. A control blend wasprepared from 40 parts of the high impact polystyrene and 60 parts ofordinary polystyrene. A portion of the extruded pellets from each blendwas molded into test bars in a screw injection molding machine.

    ______________________________________                                              % Tert-Butylstyrene                                                                           Izod impact strength                                    Blend in Copolymer    (ft. lbs./in. n.)                                                                            (°F.)                             ______________________________________                                        A     0               1.9            177                                      B     25              1.1            178                                      C     50              0.7            181                                      D     75              0.5            186                                      ______________________________________                                    

EXAMPLE 6

A mixture of 50 parts of poly(2,6-dimethyl-1,4-phenylene ether) resin(PPO), 50 parts of the blend described in Example 5 and 3 parts oftriphenyl phosphate was extruded and molded as described in Example 2.Properties of the blends are summarized in Table 4. Although impactstrength of the blends of HIPS with tert-butylstyrene copolymersdecreases steadily with increasing tert-butylstyrene content, the blendscontaining PPO in addition to the HIPS and tert-butylstyrene copolymerretained impact strength, tensile strength and ductility up to 50%tert-butylstyrene, and had higher HDT than blends containing onlypolystyrene. Ductility, tensile strength, Izod impact strength, andGardner impact strength all decreased sharply in blends made with thecopolymer of 75% tert-butylstyrene and 25% styrene.

                  TABLE 4                                                         ______________________________________                                              % Tert-                                                                       Butyl-                                                                        styrene          Tensile                                                      in Co-   Elong.  Yld.  Izod (ft.                                                                            Gardner                                                                              HDT                                Blend polymer  %       (psi) lbs./in.)                                                                            (in. lbs)                                                                            (°F.)                       ______________________________________                                        E     0        41      10,400                                                                              3.1    50     244                                F     25       30      10,000                                                                              3.0    75     252                                G     50       30      10,000                                                                              3.0    75     261                                H     75       7        8,500                                                                              1.0    <5     261                                ______________________________________                                    

The above-mentioned patents and/or publications are incorporated hereinby reference. Obviously, other modifications and variations of thepresent invention are possible, in light of the above disclosure. Forinstance, instead of poly(2,6-dimethyl-1,4-phenylene ether), copolymerssuch as poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene ether) can beused. It is, therefore, to be understood that changes may be made in thespecific embodiments described without departing from the scope of theinvention as defined by the appended claims.

We claim:
 1. A thermoplastic composition, which comprises a homogeneous,single phase admixture of:(a) a polyphenylene ether resin; and (b) acopolymer consisting essentially of styrene and from 5% to 65% by weightof 4-tert-butyl-styrene based on the total copolymer weight.
 2. Acomposition according to claim 1, in which the polyphenylene ether resinis poly(2,6-dimethyl-1,4-phenylene ether).
 3. A composition of claim 1,which comprises polyphenylene ether resin in an amount of from 10 to 90percent based on the total resin weight.
 4. A composition according toclaim 1, which further includes one or more additives selected from thegroup consisting of flame retardants, mineral fillers, reinforcements,antioxidants, dyes and pigments.